This document defines different types of advertising agencies and discusses their roles, clients, revenue sources, and industry trends. It describes full-service agencies that handle all aspects of advertising and promotion for clients. It also discusses boutique agencies, media buyers, and in-house agencies. The document outlines the roles of key agency personnel like account executives, creative directors, and producers. It explains how agencies are paid through commissions, markups, and fees. Finally, it discusses industry consolidation and how new media is challenging legacy advertising models.